1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor which has high sensitivity in a wide range of the visible ray region to the near infrared region, a process for producing the same, and an image-forming apparatus using the same.
2. Description of the Related Art
The inorganic photoconductive materials which have long been known as materials for the photoreceptive layers in photoreceptors, e.g. selenium, cadmium sulfide and zinc oxide, have some advantages. For example, they can be charged at a proper electric potential in a dark place, the electrical charge on them is hardly dissipated in a dark place, and irradiation of light makes the electrical charge on them rapidly dissipate. On the other hand, the following disadvantages are recognized. For example, in the photoreceptor produced with a selenium material, the condition of production is strict, the production cost is high, and careful handling is required since it is vulnerable to heat or mechanical shock. In the photoreceptor produced with a material of cadmium sulfide or zinc oxide type, no stable sensitivity is attained in an environment of high humidity and no long-range stability characteristic is attained since the pigment added as sensitizer yields charge deterioration by corona charge or photo-fading by exposure. On the other hand, organic photoconductive materials proposed as photoreceptive materials such as polyvinyl carbazole are more advantageous than the inor nic ones in film-forming or lightweight properties.
In making the photoreceptor of organic photoconductive material fit for practical use, a photoreceptor of function-separated type which has been proposed in order to secure high sensitivity, high durability and high stability against an environmental change includes a laminate type and a dispersion type, in which the photoconductive function is separated into a charge-generating function and a charge-transporting function. In such a function-separated photoreceptor, a wide variety of materials for the charge-generating function and the charge-transporting function can be employed, and accordingly, it is possible to select the optimal material to provide a highly efficient photoreceptor in the electrophotographic characteristics such as electrically charged property, sensitivity, residual electric potential, characteristics in repeated use, and copying durability. Moreover, it is possible to provide a photoreceptor in very high productivity at low cost because it can be produced by means of a conventional coating operation. Furthermore, the range of the photoreceptive wavelength can be optionally selected by using the material for charge-generating function.
Particularly, phthalocyanines which are highly sensitive up to the range of relatively long wavelength have been used as charge-generating materials and recently they have been employed effectively in a kind of high-speed printer, i.e. laser printer of electrophotographic system using a laser source. Examples of the phthalocyanine photoreceptors have been disclosed in Japanese Unexamined Patent Publications JP-A 58-182639(1983), JP-A60-19153 (1985) and JP-A63-267949 (1988). In JP-A 58-182639, .tau.-type and .eta.-type non-metallic phthalocyanines are used, and in JP-A 60-19153, modified .tau.-type and modified .eta.-type non-metallic phthalocyanines are used, respectively. On the other hand, in JP-A 63-267949, a mixture of .tau.-type, modified .tau.-type, .eta.-type or modified .eta.-type phthalocyanines with a butyral resin is used. In the photoreceptors prepared with these materials, however, the electrostatic characteristics such as sensitivity and electrostatic stability in repeated use are not sufficient for practical use.
Moreover, in JP-A 1-307759, an electrophotographic photoreceptor having a charge-generating layer in which a vinyl chloride type copolymer resin is used as a binder is disclosed. In such a photoreceptor, however, an electrostatic characteristic sufficient for practical use is not attained.